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Statistical classification, an application to credit default
Get PDFStatistical learning has been used in both industry and academia to create credit scoring models. These models are used to predict who might default on their loan repayments, thus minimizing the risk financial institutions face. In this study six traditional and one more recent classifier, namely kNN, LDA, CART, RF, AdaBoost, XGBoost and SynBoost were used to predict who might default on their loans. The data set used in this study was imbalanced thus sampling and performance evaluation techniques were investigated and used to balance the class distribution and assess the classifiers performance. In addition to the standard variables and data set, new variables called synthetic variables and synthetic data sets were produced, investigated and used to predict who might default on their loans. This study found that the synthetic data set had strong predictive power and sampling methods negatively affected the classifiers performance. The best-performing classifier was XGBoost, with an AUC score of 0.7732.Thesis (MSc) -- Faculty of Science, Statistics, 202
Evaluating baculovirus mixtures against false codling moth Thaumatotibia leucotreta Meyrick. (Lepidoptera: Tortricidae)
Get PDFFalse codling moth (FCM), Thaumatotibia leucotreta, is an important pest of citrus, stone fruit, avocados, peppers, and other important agricultural crops in southern Africa. Baculovirus-based biopesticides are components in an integrated pest management (IPM) programme to manage the pest in the field. Cryptogran™ and Cryptex™ which are CrleGV-SA based-biopesticides have been effective in the control of T. leucotreta for the past 15 years. Recently, CrpeNPV-based Multimax™ and Codlmax™ have been commercialised to control T. leucotreta and other important agricultural pests. Despite these viruses being relatively host-specific and safe to humans and animals in comparison to chemical insecticides, their application is hindered by their slow speed of kill, sensitivity to UV light, and the potential for insect resistance. Research investigating the effects of mixed baculoviral interactions against target pests has been a growing field of interest due to their potential to overcome such shortcomings. Previous studies using a combination of CrleGV-SA and CrpeNPV against T. leucotreta observed a reduction in lethal concentration in laboratory bioassays, indicating that such mixtures may have the potential for application in the field. This has led to the motivation to investigate further interactions between CrleGV-SA in combination with CrpeNPV, CpGV-M, and HearNPV-Au to understand better how these viruses interact and to determine whether synergistic, additive, or antagonistic interactions can occur against T. leucotreta. The outcome of these interactions will inform researchers and farmers about best practices concerning these viruses should they be combined against T. leucotreta in the future. Prior to performing mixed baculovirus infections in laboratory bioassays, oligonucleotides targeting unique regions in the viral genomes of CrleGV-SA, CrpeNPV, CpGV-M, and HearNPV-Au were designed using Primer-BLAST. The specificity of these oligonucleotides was further tested in silico using Geneious R11 software (11.1.5). The stocks of CrpeNPV, CpGV-M, and HearNPV-Au were purified using crude OB extraction from diseased C. peltastica, C. pomonella, and H. armigera larval cadavers provided by River Bioscience (Pty) Ltd (Gqeberha, South Africa). The stock of CrleGV-SA was purified using crude OB extraction from infected T. leucotreta cadavers. Subsequently, the unique oligonucleotides were used in PCR assays to detect if the samples contained the baculoviruses of interest. Amplicons of the expected sizes were generated indicating the presence of CrleGV-SA, CrpeNPV, CpGV-M, and HearNPV-Au in each of the samples. The OBs were counted using darkfield microscopy and a counting chamber before the single and mixed infections were initiated against T. leucotreta neonate larvae. Surface-dose biological assays were used to evaluate the relative virulence in terms of lethal concentration of CrleGV-SA, CrpeNPV, and CpGV-M, alone against T. leucotreta. After 7 days, the dose mortality data was analysed using “drc” in R studio and the LC50 and LC90 were compared amongst each virus. The CrleGV-SA treatment was estimated to be the most virulent in comparison to CrpeNPV and CpGV-M. A dose discriminate assay confirmed that HearNPV does not cause mortality in T. leucotreta. Similarly, the relative virulence in terms of lethal concentration of CrleGV-SA in various ratios in combination with CrpeNPV, CpGV-M, and HearNPV-Au was determined using 7-day surface dose biological assays. The CrleGV/CrpeNPV was the most virulent mixture with lower LC50 and LC90 values measured in comparison to CrleGV/CpGV and CrleGV/HearNPV, respectively. The Tammes Bakuniak graphic method confirmed the CrleGV/CrpeNPV, CrleGV/CpGV, and CrleGV/HearNPV mixtures to be antagonistic against T. leucotreta neonate larvae in terms of lethal concentration. The last aspect of the study was to determine the probable cause of larval death. A modified CTAB protocol was used to extract genomic DNA from neonate-sized T. leucotreta cadavers collected in single and mixed infection assays. The gDNA served as templates in PCR assays using the unique oligonucleotides. In single infections, the presence of CrleGV-SA in CrpeNPV and HearNPV inoculated larvae was observed. The results suggest possible covert infections of CrleGV-SA in the T. leucotreta colony which may be caused by virus infection or an unknown stress factor. The results from the mixed infections showed the presence of each virus in all replicates except for the CrleGV/CpGV and CrleGV/HearNPV mixtures. In the CrleGV/CpGV mixture, only CrleGV-SA was present in the last replicate, suggesting a possible competition for host resources. In the CrleGV/HearNPV mixture, only CrleGV-SA was detected in all 3 replicates, suggesting that HearNPV did not have any effect and the larvae died of the CrleGV-SA infection. This is the first study to report mixtures of CrleGV-SA in combination with CpGV-M and HearNPV-Au against T. leucotreta neonate larvae. Despite the antagonistic interactions observed in the evaluated mixtures, this study has laid a foundation to further investigate how these viruses interact in dual infections for the improved control of T. leucotreta. This may be done by evaluating different ratios and combinations of baculoviruses to those used in this study.Thesis (MSc) -- Faculty of Science, Biochemistry, Microbiology & Bioinformatics, 202
Thermoluminescence and phototransferred thermoluminescence of tanzanite
Get PDFThe thermoluminescence (TL) and phototransferred thermoluminescence (PTTL) properties of tanzanite, an extremely rare gem mineral, have been investigated. While tanzanite shows sensitivity to thermal and optical stimulation of luminescence techniques used for defect probing in insulators, it has received little attention in this regard. A glow curve corresponding to 70 Gy and measured at 1 °C s-1 revealed a high intensity peak at 74 °C (peak I) and two secondary peaks at 138 and 186 °C (peaks II and III). All the peaks exhibit a first order kinetics characteristics, as their positions remained unaffected by changes in either dose or partial heating ( − ). For variable doses from 10 to 200 Gy, the dose response of each peak is sublinear from the analysis of supralinearity indices. Peak I fades at room temperature when readout is delayed following irradiation, and this loss is due to thermal fading. The secondary peaks do not fade. Various methods of kinetic analysis were used to compute the kinetic parameters. For the respective peaks, the activation energy is about 0.84, 1.00 and 1.19 eV. All the peaks suffer thermal quenching with increasing heating rate. Continuous wave optically stimulated luminescence measurements were conducted to supplement the TL analysis with the aim of evaluating the kinetic parameters activation energy of thermal assistance () and quenching (). The OSL source traps are the same as the TL source traps and occur within 40 to 90 °C, 110 to 145 °C and 160 to 220 °C. The kinetic parameter when luminescence from all the source traps is considered is comparable to that when source traps within 110 to 220 °C are measured and does not depend on the dose (10, 50 or 70Gy). Except for irradiation to 10 Gy, is also comparable. For traps within 160 to 220 °C, is comparable for the different doses but higher than that of the other traps, and a similar pattern was observed for . Measurement of the PTTL signal induced by 470 nm blue LEDs following irradiation to 150 Gy and preheating to 158 °C showed that the TL peaks I and II were reproduced under phototransfer. The analysis for order of kinetics and dose response yielded the same results as the convention TL peaks. The model used to describe the PTTL intensity time response profiles shows that the PTTL emanates from a system of one acceptor and three donors, where the latter is a conglomerate of an unknown number of peaks.Thesis (MSc) -- Faculty of Science, Physics and Electronics, 202
Teaching problem solving: the "Ten Commandments" approach
Get PDFThe evident need for an intervention to help physics students, especially incoming university students, develop their problem-solving skills led to exploring possible curriculum structures to achieve the goal. A modified curriculum structure of the first-year physics course, including explicit teaching of physics problem solving, was developed and implemented at Rhodes University, South Africa, in 2017. First-year physics students learn to solve problems by implementing the "Ten Commandments" of physics problem solving in their solutions, following a three-stage problem-solving framework. Additionally, students attend whiteboard tutorial sessions where they actively practise using the problem-solving framework in their solutions to physics problems with peers in an environment where help is available. Students are explicitly prompted to use the \Ten Commandments" during the whiteboard tutorials and not prompted for other assessment tasks. Students' solutions to formative physics assessment tasks (problem sets and tests) in the first semester were examined, problem-solving scores were determined using a problem-solving rubric developed in the department, shifts in attitudes and beliefs about physics and solving problems in physics were measured, and relationships between their problem-solving scores and task performance were evaluated to investigate how students adopted the framework and its implications over one semester. The problems issued to students differed in context and difficulty level; as a result, not all of the "Ten Commandments" were applicable to solve all problems, and different combinations of the commandments were applied to different problems. The explicit use of the problem-solving rubric to mark student problem sets was an indirect prompt for students to use commandments when doing their problem sets. As a result, students attempted to implement more applicable "commandments" (mostly partially correct) in their solutions to problem sets than in tests. Moreover, students' solutions to problems show that they used more of the "commandments" they were familiar with from school and less of the new ones, such as drawing diagrams without being prompted, producing algebraic solutions before substituting numbers, and doing dimensional analysis. Problem sets are often assumed to help prepare students for tests; however, correlations between students' problem-solving scores and performance between the two assessments did not give clear indications of whether problem sets were helping to prepare students to solve problems. Lastly, students' attitudes and beliefs also show a negative shift in students' perceptions of problem-solving by the end of the first semester. Problem-solving is a skill that develops in stages and over time; therefore, a timeframe longer than one semester is needed to report on significant changes in students' problem-solving habits and perspectives about problem-solving in physics. The study results are also important in giving insights into the initial developments of problem-solving skills and teaching problem solving.Thesis (MSc) -- Faculty of Science, Physics and Electronics, 202
Investigating optoelectronic and thermal properties of perylene tetracarboxylic bisimide derivatives-and-cellulose nanocomposites for possible solar energy applications
No full textRestricted access. Expected release in 2026.Thesis (MSc) -- Faculty of Science, Chemistry, 202
The reading to learn pedagogy in South African inclusive English First Additional Language classrooms: successes and challenges
Get PDFReading to Learn (RtL) has been frequently suggested for students not meeting grade-appropriate reading standards. However, its achievements and shortcomings have not been examined in inclusive education. In light of this, the main goal of this study was to explore the successes and challenges of this methodology in grade 9 English First Additional Language (FAL) inclusive classrooms across four schools in the Northern Cape Province’s John Taolo Gaetsewe District. In light of the grave concerns about literacy development in South African schools, this methodology was created to fulfil the literacy needs of students from underprivileged groups in Australia. This qualitative study was grounded in social constructivist theory and an interpretative paradigm. The research used an exploratory case study comprising four participants who were purposively recruited and empowered with RtL between 2016 and 2022. The data-gathering methods used were semi-structured interviews, focus group discussions, and classroom observations to get insights into the achievements and shortcomings of the RtL pedagogy in inclusive classrooms. The qualitative data in this study was analysed using thematic analysis. The study’s findings revealed that the RtL pedagogy gave students who faced reading obstacles in inclusive classes the skills needed to read, read with meaning, and improve as readers and writers through its six-step scaffolding interactive cycle. There were challenges in employing the RtL pedagogy in inclusive classes, such as it is time-consuming and makes it difficult for teachers to adhere to the time frame stipulated by the annual teaching plan. Nevertheless, the study’s findings showed that the advantages of the RtL pedagogy outweigh the challenges.Thesis (MEd) -- Faculty of Education, Institute for the Study of Englishes of Africa, 202
Evaluation of education quality in the Edulink education for sustainable development training programme in Namibia
No full textRestricted access. Expected release 2026.Thesis (MEd) -- Faculty of Education, Primary and Early Childhood Education, 202
Vulnerable Youth or Vulnerabilising Contexts? A Critical Review of Youth Sexual and Reproductive Health and Rights (SRHR) Policies in Eastern and Southern Africa
Get PDFPolicy decisions about young people’s sexual and reproductive health and rights (SRHR) have far-reaching implications for their well-being. Few SRHR policies, however, focus specifically on youth. Rather, youth SRHR tends to be subsumed within national policies of Health, Youth, Education and Development Ministries, particularly in the Eastern and Southern Africa (ESA) region, complicating an assessment of the overall state of youth SRHR policies. Given the fact that youth SRHR policies focus on a particular segment of the population—youth, teenagers or adolescents—how policies depict these subjects has implications for how policy objectives, programmes and interventions are conceptualised and the kind of sexual and reproductive health concerns that are prioritised
Regimes of truth regarding ‘sexual justice’ in academic literature from 2012 to 2022: a scoping review
Get PDFThe notion of ‘sexual justice’ has gained traction in academic and policy arenas in recent years. This paper presents a scoping literature review of the regimes of truth, following Foucault, of ‘sexual justice’ appearing in the scientific literature from 2012 to 2022. Thirty-eight papers were coded using (1) content analysis of the studies’ central problematics, the programmes referred to, and institutional location(s); and (2) thematic analysis of how the notion was deployed. Central problematics centred on (1) critiques of, or alternatives to, dominant approaches to sexual and reproductive health; and (2) highlighting injustices. As such, ‘sexual justice’ is fighting for legitimacy in the truth stakes. There is a distinct paucity of papers tackling the translation of ‘sexual justice’ into practice. South Africa dominates as the site in which papers on ‘sexual justice’ have been produced, but there is a lack of South-South collaboration. Two themes were apparent around which conceptions of sexual justice cohere. Firstly, sexual justice is seen as a vital, yet politically ambivalent goal, with neoliberal co-optation of progressive rights agendas being warned against. Secondly, sexual justice is viewed as a means, in which sexual justice is described as having potential to repair established frameworks’ shortcomings and oppressive legacies
Plankton and macroinvertebrate dynamics in the Khakhea–Bray transboundary aquifer region
Get PDFTemporary wetlands are prevalent in semi–arid and arid climates across the globe and harbour unique faunal assemblages that significantly contribute to regional aquatic biodiversity. This study aims to enhance our understanding of the ecological dynamics of temporary wetland ecosystems, focusing on plankton dynamics, large branchiopod diversity, trophic dynamics, water quality and the impacts of freshwater salinisation in temporary pans in the Khakhea Bray Transboundary aquifer region in the North west Province, South Africa. This body of work represents field, laboratory and writing components which span the period May 2021 to December 2023. The results from this study revealed seasonal patterns in plankton diversity with a winter peak in phytoplankton diversity dominated by Zygnematophyceae species, while Chlorophyceae were dominant in summer. Zooplankton diversity was high in summer as compared to winter, with both Rotifera and Copepoda dominant in both seasons. Six large branchiopod species were found in the region, and three of these were new distribution records for the North west Province, including the first record of Phallocryptus spinosa in the salt pan that was sampled in summer. Large branchiopod diversity was mainly influenced by water temperature and phosphorous in summer, while sediment sodium influenced the diversity in winter. The stable isotope analyses used to determine trophic dynamics in these temporary pans revealed that the food web had four trophic levels, with the top predators being the notonectids Anisops sp. The dominant consumers were predatory insects such as Sigara sp., Anisops sp., Lestes sp., Rhantus sp. and Cybister sp. adults and larvae, as well as detritivorous Tomopterna sp. tadpoles. High trophic niche overlaps were found between the notonectids and the dytiscids. These temporary pans are susceptible to anthropogenic impacts, and disturbed pans were found to have elevated pH, ammonium, phosphates and dissolved oxygen compared to the undisturbed pans. A strong positive relationship was observed between chl–a and temperature, pH, dissolved oxygen, phosphates and ammonium. Chlorophyll–a concentration increased as surface area and the distance from kraals, buildings and latrines decreased. Freshwater salinisation was found to cause notable shifts in abiotic factors and benthic phytoplankton communities, favouring the proliferation of saline–tolerant diatom species at the cost of more sensitive taxa. The study also revealed that in interaction with salinisation, time also exerted a notable influence on shaping the benthic phytoplankton community. Salinity levels of 2.5 ppt and above led to significant decreases in emergent taxa richness and abundance, with Spinicaudata and Ostracoda being the most sensitive taxa to high salinities. There was a limited effect on community hatching phenology dynamics from salinity. This suggests that the main impact of salinisation in these systems will be reductions in hatching success and, hence, reduced recruitment. The study highlights the vulnerability of temporary pan ecosystems to anthropogenic influences and the complexities of interactions of organisms and the environmental conditions in these systems.Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 202